Safe to say there's some difference between the Zuiko and Sekor lenses (even if they're the same element count/layout, they'll differ slightly in prescription and glass selection). FWIW, I've got the Zuiko on my Mamiya Six (6x6/6x4.5 with captive mask leaves, red window only, no viewfinder mask that I've found), and I've never seen any reason to dislike the Zuiko lens -- I've got a couple Olympus Pen EE family cameras with Zuiko lenses, too, and they're excellent.
I'm not even sure what model I have, but I think it's done by features (other than the Automat which is clearly marked as such).